Characterization of an Aqueous Flow Battery Utilizing a Hydroxylated Tetracationic Viologen and a Simple Cationic Ferrocene Derivative

Abstract

Herein, a new semi‐organic aqueous flow battery based on a hydroxylated tetracationic viologen, 1,1′‐bis(3‐((2‐hydroxyethyl)dimethylammonio)propyl)‐[4,4′‐bipyridine]‐1,1′‐diium tetrachloride ([(DMAE‐Pr)2‐Vi]Cl4), and the ferrocene derivative, (ferrocenylmethyl)trimethylammonium chloride (FcNCl), is demonstrated. Efficiency, accessible capacity, and capacity retention of the battery are investigated at two concentrations of the active redox species: 0.1 and 0.5 mol dm−3 in 1 mol dm−3 KCl near‐neutral electrolytes. The implementation of the ferrocene‐derivative posolyte decreases the capacity fade rate by a factor of ≈4 with respect to previous work using 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPOL) as posolyte. Capacity loss is driven by crossover of the positive redox couple into the negolyte, in particular at high concentrations, indicating the need for more selective membranes and less permeable ferrocene derivatives. Discussions are supported by conductivity measurements, cell resistance, and postmortem analysis of the electrolytes using cyclic voltammetry and nuclear magnetic resonance (NMR) spectroscopy. The characterization of [(DMAE‐Pr)2‐Vi]Cl4 is expanded as a high‐energy negolyte and future scaleup requirements for aqueous organic flow batteries are informed.

Comparison of the Influence of Oxygen Groups Introduced by Graphene Oxide on the Activity of Carbon Felt in Vanadium and Anthraquinone Flow Batteries

“…The observed effect of rGO-modified electrodes in the overall flow cell performance shows promise to tackle one of the main challenges in OFBs, that is, the limited operational current (and power) density compared to vanadium systems resulting from high area-specific resistance, which is a consequence, in most cases, of poorly conductive aqueous electrolytes and resistive ionic exchange membranes . Combined with relatively high reactant costs and capacity retention, low currents represent an important techno-economic challenge for OFBs. , Indeed, the energy efficiencies of VFBs can routinely achieve values close to 80% for rectangular-channel flow cells operating at 200 mA cm –2 .…”